Short and long term administration of vasodilator drugs to patients with pulmonary artery hypertension (PAP) effects small falls of PAP and larger reductions of pulmonary vascular resistance due to increases of cardiac output. Side effects of systemic hypotension are sometimes troublesome. Improvement of survival has not yet been demonstrated. It is likely that any treatments capable of sustained clinical benefit in hypoxic cor pulmonale will have to arrest or reverse pathology in the airway and pulmonary vessel. There is no evidence that pulmonary vasodilator drugs will do this. Their clinical place is in doubt.